#Definition for a binary tree node.
#class TreeNode(object):
#    def __init__(self, x):
#        self.val = x
#        self.left = None
#        self.right = None
class Solution:
    def mergeTrees(self, t1, t2):
        """
        :type t1: TreeNode
        :type t2: TreeNode
        :rtype: TreeNode
        """
        if t1 is None:
            return t2
        if t2 is not None:
            t1.val += t2.val
            t1.left = self.mergeTrees(t1.left, t2.left)
            t1.right = self.mergeTrees(t1.right, t2.right)
        return t1
